Ok, Here's what you should do. After they spawn and the fry have been free swimming for ten days remove the parents and move them to the 20L with their favorite piece of decor. Then after they spawn in the 20L and the fry have been free swimming for ten days move them back to the 30. You can either get another tank to move the fry to or give the fry to whatever is eating them....
Fry can "vanish" for many reasons. . Some fry just don't make it, they fall ill and die from poor water quality , they just don't eat enough (this can happen no matter what you do to prevent it) something else in the tank sneaks a snack here and there , the fry were just weak , the parents cull their fry to get rid of the ones that are deformed or not up to snuff in their eyes. Cons are great parents give them time and you'll have about a million of them in no time. The first spawn or two is just a breaking in period, after that it's non stop baby cons. You have been warned :lol: :lol: :lol: :lol:
Be prepared for some aggression from the male directed at the female. My fist convict spawn I had to move the female with the fry because the male beat her up so badly. I lost her for a few days and thought she had jumped behind the tank, but then I found her in the floating plants battered but alive. That was in a 20L.
I have a pair that just spawned today in a 110 and the opposite is true, The female wont let the male anywhere near her or her nest. Its rather comical actually.